Occurrence
On 24 September 2015, Shaheen Air International flight SAI791, a Boeing 737-400 registration AP-BJR, departed Sharjah International Airport for Bacha Khan International Airport, Pakistan. At 0239 local time, the aircraft took off from taxiway Bravo instead of runway 30. The air traffic controller lost visual watch on the aircraft as it taxied from taxiway Alpha 20 towards taxiway Bravo and regained sight when it passed the intersection with taxiway Alpha 18. The controller did not stop the takeoff roll. After takeoff, the flight crew was not informed about the incident; they learned of it from the operator five days later.
Investigation
The Air Accident Investigation Sector (AAIS) of the UAE was notified four days after the incident. Flight data and communications confirmed the aircraft turned onto taxiway Bravo and departed from there. The investigation could not determine why the flight crew did not notice they had lined up on a taxiway. The flight crew stated they had no doubt they were on the runway and did not question visible cues including lighting.
Cause
The AAIS determined the cause of the incident as: "most probably, the flight crew did not devote sufficient attention to the taxi route, or taxi route lighting and signage. The flight crew misunderstood the air traffic control instructions and failed to identify that the Aircraft had been aligned on a taxiway, instead of on the runway, resulting in a takeoff from the taxiway."
Contributory Factors
The report listed several contributory factors, including the operator's standard operating procedures not requiring verification of correct runway lineup, early takeoff clearance, the controller's urgency, the red stop bar lights being off, brighter green lead-on lights for the taxiway, similar numeric designations, the controller losing visual watch, and the possibility the crew assumed the taxiway was the runway due to its width.
Safety Recommendations
The investigation issued safety recommendations to Shaheen Air International, Sharjah Aerodrome, Sharjah Air Traffic Services, and the UAE General Civil Aviation Authority.